1. Field of the Invention
The inventions described below relate generally to the field of in vivo surgical field illumination during medical and surgical procedures.
2. Background of the Invention
Illumination of body cavities for diagnosis and or therapy has been limited by overhead illumination. High intensity incandescent lighting has been developed and has received limited acceptance as well as semiconductor and laser lighting, however these light sources have a heat and weight penalty associated with their use. Excessive heat can cause unwanted coagulation of blood, as well as unnecessarily heating of a patient's body. Additionally, heat buildup can cause various components fabricated from some polymers to exceed their glass transition temperature and deform. Heat buildup may also cause optical properties of various components to be compromised. Weight of some illumination systems makes them uncomfortable for an operator, especially during a lengthy procedure. Conventional light sources rely on fiber optic and similar waveguide materials to conduct light to a body cavity. Conventional waveguide materials that are suggested for medical use suffer from some of the unstable transmission characteristics under extended use described above, and their transmission characteristics may also change when sterilized using conventional techniques (e.g. autoclave, EtO, gamma or e-beam irradiation). Additionally, precision optical polymers have limited mechanical properties which limits their application in medical/surgical situations.
Examples of conventional polymers that have traditionally been used with some success in surgical illumination systems include acrylics such as polymethylmethacrylate (PMMA) and polycarbonates (PC) such as Lexan®. Polycarbonate is desirable since it may be fabricated into various configurations which may be slightly bent without shattering. While polycarbonate has good mechanical strength and manufacturability, its optical properties are not optimal. For example, polycarbonate has a low light transmission efficiency, and therefore is not ideal for transmitting light, especially along a long pathway. Acrylic has also been used with some success in surgical illumination systems. It is more efficient at transmitting light than polycarbonate, is easy to process (e.g. may be injection molded), but acrylic is also brittle and can shatter. Also, acrylic has a relatively low glass transition temperature, and thus acrylic components do not tolerate heat buildup well, especially in medical illumination systems where heat is generated during use. Acrylic also absorbs moisture and this changes the refractive index of the material which can alter its performance. Therefore, it would be desirable to provide a material that is better suited for medical illumination systems and that has at least some of the desirable mechanical and optical properties of acrylic or polycarbonate while minimizing the less desired properties. For example, such materials would preferably have equivalent or better light transmission efficiency than acrylic, a higher glass transition temperature relative to acrylic, be easy to process like acrylic or polycarbonate, have better resistance to moisture absorption than acrylic, and be bendable without shattering like polycarbonate. Moreover, the material used must also be able to withstand terminal sterilization without compromising optical properties. Many polymers discolor when irradiated or can deform due to exposure to heat during sterilization. It would therefore also be advantageous to provide a material that can be terminally sterilized without damage. Also, any materials used in a medical application must also be biocompatible. At least some of these challenges will be addressed by the exemplary embodiments disclosed below.